Virtual Private LAN Service (VPLS) is a proposed standard that would allow private local area networks (LANs) to be established over a public network. The VPLS presents an Ethernet interface to the users. Bridging is done at Provider Edge devices (PEs), such that the core public network need not know that a VPLS is being set up. The core network must simply guarantee the reachability of the VPLSs between the PEs.
VPLS as currently defined requires that the core network be a MultiProtocol Label Switching (MPLS) network. Once the PEs are configured with VPLS identifiers (IDs), the MPLS core network allows automatic advertising between the PEs. Each PE advertises to other PEs which VPLS IDs are supported by the PE, and advertises a MPLS label which other PEs can use to communicate with the PE with respect to each particular VPLS ID. As this VPLS ID to MPLS label mapping information is shared among multiple PEs that advertise the same VPLS ID, a mesh of MPLS label switched paths is generated to interconnect all the PEs involved in each VPLS.
Several service providers have already established large Asynchronous Transfer Mode (ATM) networks. In order to implement VPLS (as currently defined by the Internet Engineering Task Force) over an ATM network, service providers would have to add an MPLS signaling protocol to the ATM network, which would be costly and operationally challenging. An alternative would be to emulate VPLS over an ATM network using a mesh of virtual circuits. However, a significant problem for a service provider wishing to emulate VPLS over an existing ATM network is the inability to automatically establish the mesh of connections between PEs providing the bridging for the VPLS. ATM nodes advertise reachability information using a Private Network-Network Interface (PNNI) routing hierarchy, defined in ATM Forum Technical Committee, “Private Network-Network Interface Specification, v.1.1”, af-pnni-0055.002, April 2002. Under PNNI, each ATM node belongs to a peer group. An ATM node advertises its reachability information to all nodes within its peer group, but only the peer group leader advertises this information outside the peer group. Furthermore, the information advertised by the peer group leader to nodes outside the peer group is limited. There is currently no means by which an ATM node can advertise VPLS ID support to nodes outside its peer group. This means that an owner of an ATM network cannot offer VPLS-like services to customers, without either tedious manual configuration of virtual channels for each pair of PEs and for each VPLS ID, or adding an MPLS signaling protocol to the network.